The development of optical communication systems has led to considerable activity in the optical device field. Various devices are of importance in optical communication systems, including sources (light-emitting diodes, lasers), transmission media (optical fibers) and detectors. The quality and characteristics of these devices (as well as other devices in the system) contribute significantly to the quality and efficiency of the optical communication system.
A particularly important part of the optical communication system is the photodetector. It contributes significantly to the sensitivity of the receiver in an optical communication system and often determines repeater spacing of an optical communication system. Particularly important is the noise generated at the photodetector and the bandwidth of the photodetector.
In certain wavelength ranges, photodetectors are made with compound semiconductors containing phosphorus. For example, for many photodetector devices operating at about 1.3 .mu.m (i.e., the 1.25-1.35 .mu.m region), InP is conveniently used as a substrate material and an epitaxially grown material such as InGaAs is used as the active material. In such devices, low noise is particularly important especially where these photodectors are used in optical communication systems.
An especially important source of noise in photodetectors is dark current. It is highly desirable to minimize dark current in photodetectors because it adversely affects noise performance. Improved noise performance makes possible improved performance in a variety of optical systems including optical communication systems.